Reasonable Degree of Medical Certainty

The ritualistic words “reasonable degree of medical certainty” (RDMC) are intoned by medical expert witnesses in most state and federal courts.  Courts in some liberal states, such as New Jersey, courts may dilute the typical formulation to require that expert witnesses opine with “reasonable degree of medical probability,” but the magic words are just as important.

Do the words have any meaning?

The words certainly have functional meaning in that their omission may lead to untoward consequences.  Although I have not seen many reported decisions on the issue, I have seen grown men cry when their adversaries pointed out that their expert witnesses failed to utter the magic words, and their trial judges seriously pondered striking the unadorned testimony.  In one case, my adversary begged me for a stipulation because his witness had failed to use the magic words, and had already fled the jurisdiction.  Because I (correctly) believed that the trial judge was going to grant a directed verdict on another ground, I cheerfully agreed to the stipulation that the witness, if he had been asked, would have stated that his opinions were all held and expressed to a RDMC.

Do the words have actual meaning besides the operational significance of being required by law?

David Faigman, who is truly a distinguished Professor, at the University of California Hastings College of Law, writes that the use of these words is an empty formalism.  The expression used in conjunction with a claim that X causes Y, or that X causes this particular case of Y, “has no empirical meaning and is simply a mantra repeated by experts for purposes of legal decision makers who similarly have no idea what it means.”  Faigman, “Evidentiary Incommensurability:  A Preliminary Exploration of the Problem of Reasoning from General Scientific Data to Individualized Decision-Making,” 75 Brooklyn Law Review 1115, 1134 (2010).  Faigman goes on to note that “less extreme versions” of RDMC attached to propositions about the causation of individual events are objectionable as well.  Faigman appears to take aim at both the RDMC qualifier as well as the assertion of some empirical propositions that are qualified by it.

In part, Professor Faigman’s concern about the lack of “empirical meaning” for some statements of individual causation are well taken.  He asks, for example, how can a witness say “more likely than not” that a given instance of cross-race identification is inaccurate. “Experts’ case-specific conclusions appear to be based largely on an admixture of an unknown combination of knowledge of the subject, experience over the years, commitment to the client or cause, intuition, and blind-faith.  Science it is not.” Id. at 1134 – 35.  Faigman gives other examples of the problem in the context of specific medical causation in personal injury cases, which illustrates that clinical training and practice often provide no basis for reliable attribution of causation in particular cases.  Id. at 1132 (“the core nature of clinical practice is at right angles to the crux of most legal inquiries); id. at 1133 & n.45 (citing Henricksen v. Conoco-Phillips Co., 605 F.Supp. 2d 1142 (E.D. Wash. 2009) for the proposition that differential etiology is useless when there is a large percentage of idiopathic cases and no discriminating feature of toxic causation in plaintiff’s case).

To the extent that Faigman has identified an embarrassing “lacuna” in the use of scientific evidence in courtrooms, his article is, as his articles usually are, an astute commentary on the sad state of how science is applied in court rooms.  Faigman, and a few other academic lawyers, have been willing to point to the naked judges and juries and boldly note that they are without clothes.

But is Faigman correct that the expression, RDMC, “is simply a mantra repeated by experts for purposes of legal decision makers who similarly have no idea what it means”?  Id. at 1134.

Faigman’s critique of RDMC appears to be aimed at expert witnesses who will utter the phrase, (and at courts that will superficially accept the utterance), without understanding the phrase, or perhaps not really meaning or caring what they say.  See generally H. Frankfurt, Bullshit 2005 (passim).  Surely, however, the phrase is not semantically empty.  “Certainty” has clear epistemic connotations and implications for the witness’s opinion, both in terms of his own state of mind, and in terms of the empirical support the witness has for his opinion in the form of reasonably relied upon data, and sound inferences to a reliable conclusion.  Subjectively, the witness who utters the phrase acknowledges that he is not speculating and that he believes that his opinion satisfies professional standards for claims of knowledge.  A witness who qualifies his opinion with these “magic words” communicates his willingness to put his professional reputation on the line, and to defend the opinion before his peers.  Objectively, the phrase conveys the notion of reliable knowledge.  To be sure, human beings may not enjoy “certainty” in their knowledge of empirical propositions, but the “reasonable” qualifier makes the entire phrase meaningful and important.  Even if judges and lawyers were to take the phrase as empty (because they are inured to bullshit in this setting), jurors are likely to take it as having a plain language meaning that adds epistemic and personal “heft” to the opinion.

Furthermore, Faigman’s comment about RDMC is inaccurate in some states that take the utterance very seriously.  In Pennsylvania, for instance:

“the expert has to testify, not that the condition of claimant might have, or even probably did, come from the accident, but that in his professional opinion the result in question came from the cause alleged. A less direct expression of opinion falls below the required standard of proof and does not constitute legally competent evidence.”

Menarde v. Philadelphia Transportation Co., 376 Pa. 497, 103 A.2d 681, 684 (1954).   This “formalistic” requirement in Pennsylvania is particularly important because the appellate courts have seriously eroded the gatekeeping function under Pennsylvania Rule of Evidence 702.  The epistemic requirements of RDMC are thus, for the time being, the only way to ensure that science adequately informs the verdicts and judgments of Pennsylvania courts.

Professor Faigman’s article raises an additional, “case-specific” concern.  For reasons that are unclear, Faigman uses the connection between asbestos and mesothelioma to serve as an example of an outcome that has a unique cause:

“An example of this is the relationship between asbestos exposure and mesothelioma. The unique cause of mesothelioma is exposure to asbestos, but not everyone exposed to asbestos develops mesothelioma.”  Id. at 1120.


“In the example of mesothelioma, a civil plaintiff who has this disease will be able to trace it back to asbestos exposure.”  Id. at 1121.

Not really.  Faigman offers no support for these startling assertions, and they are wrong.  Mesothelioma is known to be caused by erionite, a non-asbestos zeolite mineral, and the disease is probably caused by radiation as well.  Young adult cases among survivors of childhood Wilms’ tumor have been frequently described (after therapeutic radiation).  There is much that is known and unknown about mesothelioma causation.  Some forms of asbestos clearly cause mesothelioma, but there are few competent experts who will say, with RDMC, that all cases of mesothelioma are caused by asbestos.

Comments are closed.